Magnetic and optical data disks are used to store a large quantity of data. The information is stored on at least one major planar surface of the disk, allowing the information to be accessed when the disk is secured to a spindle clamp for high-speed rotation of the disk. Spindle clamps are also referred to as “disk clamps” and “disk chucks.”
In the quality control testing as well as the manufacturing of magnetic and optical data disks, rapid robotic removal of a tested disk from a spindle is followed by replacement with a disk to be tested or processed. A suitable spindle is described in U.S. Pat. No. 4,755,981 to Ekhoff. The spindle clamp of Ekhoff includes movable jaw segments which slide along a centrally positioned cone to expand the arrangement of jaw segments when a disk is to be clamped and to contract the arrangement when a disk is to be released. Thus, a collet-type mechanism is used to secure the disk at its central opening. The function of the spindle clamp is to secure the disk in a tightly concentric manner, while introducing minimal distortion or waviness to the precision planar surfaces of the disk. Because of the high volume of disks involved and the short period of processing time, it is important that this clamping/unclamping function occurs reliably and without any required secondary actions, such as attaching a removable cap with a screw. In the device described in the Ekhoff patent, the primary holding force is applied to the disk in a radial fashion as the three jaw segments slide downwardly along the cone under the influence of a spring located on the underside of the clamp. The movement of the jaw segments along the cone is controlled by connection to a cap, which consists of an axially extending post having an upper head. The stroke motion is applied to the post either pneumatically or mechanically. Slippage of the disk is controlled by the force that is applied as the jaw segments are wedged between the inside circumference of the disk and the cone along which the jaw segments slide.
The ability of a spindle clamp to secure a storage disk is limited by the processing tolerance to distortion introduced into the disk, as well as by the point of slippage of the jaw segments against the inner cone. This point of slippage is primarily affected by the level of lubrication which is introduced in order to control particle generation that would occur through wear processes. Another concern is that spindle clamps used in quality control and other such processing should be designed to handle disks with different configurations and thicknesses, without introducing distortions due to variations in contact between the jaw and the disk inside diameter and the resulting load concentrations.